1. Field of the Invention
This application is a 371 of PCT/EP97/01028, filed Mar. 1, 1997.
The present invention subject matter of the invention concerns a composition for permanent hair-styling, characterized in that as a keratin-reducing agent it contains a compound of the general formula ##STR2## in which A stands for --CH.sub.2 --, C.dbd.O, --S--, --O--, --NR--, where R=C.sub.1 to C.sub.6 alkyl or C.sub.1 to C.sub.6 hydroxyalkyl, n stands for an integer from 0 to 3, on the condition that n stands for zero only if A=--CH.sub.2 --, and m stands for an integer from 1 to 3, and to a method for permanent hair-styling using such means.
2. Prior Art
The classical technique for achieving permanent hair-styling is known to be based on two treatment steps: In the first step, the cystine disulfide bridges of the keratin in the hair are opened by the action of a composition that includes a reducing agent (styling means). The hair is then put in the desired style. In a second step, cystine disulfide bonds are closed again, using a fixative, that is, an agent that contains an oxidizing active ingredient.
As the pioneering work in German Patents 948186 and 972424 show, thioglycolic acid, for instance in the form of an ammonium or monoethanolamine salt, is used as a classical permanent-wave reducing agents. Other typical reducing active ingredients are inorganic sulfites, 2-mercaptopropionic acid (thiolactic acid), 3-mercaptopropionic acid, certain mercaptocarboxylic acid esters, cysteine, and derivatives of these compounds.
However, all of these composition and agents have a number of disadvantages. Alkaline preparations on the basis of mercapto acetamides, despite adequate action, cause hair damage, which is expressed for instance in increasing hair breakage. Often, these composition and agents also undesirably stress the scalp.
Finally, the unpleasant smell of the reducing agents used requires intensive perfuming of the products. Using 2-mercaptopropionic acid (thiolactic acid) allows one to solve some of these problems. However, thiolactic acid in comparison with the generally used thioglycolic acid is distinguished by weaker shaping action.
The mercaptocarboxylic acid esters that allow hair-styling even at relatively low pH values are not satisfactory in terms of their coloration by the skin and their risk of sensitization. Instead of mercaptocarboxylic acid esters, mercaptocarboxylic acid amides have also been used, such as thioglycolic acid amide or alkyl- or hydroxyalkyl-substituted mercaptocarboxylic acid amides. These substances, like the mercaptocarboxylic acid esters, have a high shaping potential even at relatively low pH values, but with regard to sensitization are even more critical than the mercaptocarboxylic acid esters.